Page 194 - Quantitative Imaging of Small Tumours with Positron Emission Tomography

Response assessment with [18F]DCFPyL and [18F]FDHT Conclusion In conclusion and in addition to the results of Werner et al., in patients harboring a small tumour load no relevant sink effect of [18F]DCFPyL is to be expected. However, for patients with larger tumour volumes a sink effect may in fact occur, meaning personalized dosimetry of 177Lu-PSMA radioligand therapy might be needed for these patients. For [18F]FDHT, a similar sink effect of tumour load can be expected. Hence, there indeed seems to be a general effect for radiotracers that have a specific targeting, rendering use of SUV for such tracers invalid. We urge colleagues currently using both [18F]DCFPyL and 177Lu-PSMA radioligand therapy to repeat the study by Werner et al. in patients with a clinical indication for 177Lu- PSMA radioligand therapy. Moreover, since a clear definition of small versus large tumour load is not established, future studies should refrain from using SUV for quantification of tumoural [18F]DCFPyL uptake and resort to using TBR instead (4). For [18F]FDHT, use of SUV should be avoided regardless of tumour load, but more specifically in high-volume patients in response assessment settings. 9 193